Electrical heating unit and method of making same



F. J. EWALD ELECTRICAL HEATIhiG UNIT AND METHOQOF MAKING SAME June 11, 1957 Filed Jan. 25, 1954 INVENTOR. FRED Eh AL D BY 7 arroeA/fys- Unitd States Patent ELECTRICAL HEATING UNIT AND NEETHOD OF MAKING SAME Fred J. Ewald, Hinsdale, 111., assignor to Tuttle & Kift, Inc., Chicago, 111., a corporation of Illinois Application January 25, 1954, Serial No. 405,872

8 Claims. (CL 20167) This invention relates to electrical heating units of the type in'which a tubular metallic sheath encloses a hard packed electrical insulating material which supports a resistance heating element on the longitudinal axis of the sheath within the latter. As ordinarily produced, heating units of this kind are provided with a relatively fine extremely high resistance'unit throughout the major portion of'their length, but at the ends thereof where connection is to be made to the lead-in cables and the like, the relatively fine high resistance unit is connected in series to a much heavier low resistance lead which then extends'from the end of the resistance unit and to which connection may thus be made with the lead-in cable.

The present invention is primarily concerned with the formation of the ends of such resistance or heating units whereby when a workman seeks to install the same he may with a minimum of effort remove the sheath and the insulating material from the terminal portion of the lead at the end ofthe heating 'unitto prepare for the connection which must be made between such lead and the lead-in cable.

There are a number-of problems in connection with the removal of the sheath and the insulating material. 'In the first place the sheath must be cut so as not to dam age the lead-in wire centrally thereof. This is no easy task if left to the workman himself because the sheath is usually of a hard material such assteel. Furthermore, the hard packed, insulation must be removed from around the center lead without damaging the lead and without damaging the remainder of the insulation which should remain intact. Prior art efforts directed toward the preliminary preparation of the ends of such heating units so that they might be readily shipped in the field have not been particularly successful because the heating units thus preliminarily prepared are ordinarily subjected to rough handling from the time they are made until the workman receives them for installation.

It is a principal object of this invention, therefore, to provide a method of preparing the ends of heating units of this kind so that the workman when he installs them may bare the end of the conductor centrally of the unit with a minimum of effort and without disturbing the remaining structure of the heating unit even in the area closely adjacent the end which is thus bared.

Other objects of the invention will appear as the description proceeds.

To the accomplishment of the foregoing and related ends, the invention, then comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawing setting forth in detail one illustrative embodiment of the invention, this being indicative, however, of but one of the various ways in which the principle of the invention may be employed.

In said annexed drawing:

Fig. 1 is a side elevational view broken and partially the terminals of the heating unit illustrated in Fig. 1

taken on a plane substantially indicated on the line 2-2; Fig. 3 is a side elevational view similar to Fig. 2 but showing such terminal at one stage of the process which comprises this invention;

Fig. 4 is a transverse sectional view of the structure illustrated in Fig. 2 taken on a plane substantially indicated by the line 44;

Fig. 5 is a transverse sectional'view of the structure illustratedin Fig. 3 taken on a plane substantially indiappliances such asstoves,-ovens and the like. The tubucated by the line 5 -5;

Fig. 6 is a transverse sectional view of the completed terminal after the operation of the process of the present invention and takenon a plane substantially like that of Fig. 4, line"4-4; and i I 3 Fig. 7 is aside elevational view drawn to an enlarged scale of a terminal of the heating unit such as illustrated in. Fig. 1 after the sheath and insulation have been stripped therefrom as would be done by workmen installing such unit.

Referring now more 'specifically'to the drawing and more especially to Fig. 1, there is'here illustrated a heat- "ing unit which is generally U 's hap'ed and which comprises an' outer'sheath generally indicated at 1. The sheath 1 is tubular, and while illustrated as U-shaped in Fig. l, may"take on any desired configuration. Heating units of this kind are commonly employed in domestic lar sheath 1 is filledwith a hard packed insulating material which supports centrally of the tubular sheath 1 a resistance heating element generally indicated at Z-in Fig. 1. This resistance heating element throughout the major portion of the axialextent of the tubular sheath 1 is generally a relatively fine high resistance wire. It

would be impractical to have the resistance wire 2 extend from the end of the heating unit for connectionto "the lead-in cable since great care must be exercised when making anelectrical connection with a fine heating element of this type. Accordingly, the heating element is fabricated during manufacture by carefully connecting the high resistance element 2 to a larger diameter low resistance lead-in wire generally indicated at 3 which occurs fora short distance at each end'of the resistance unit.

It is to this largerleaddu wire 3 that the workman makes connection when he installs a heating unit of this kind in an appliance such as a stove.

For reasonsof economy and high standard of quality in the manufacture of units of this kind, the central lead 3 and the tubular sheath 1 and the insulating material hard packed around the lead 3 within the tubular sheath 1 are made continuously so that the three elements just described terminate in a single plane generally indicated at 4.

Before the resistance unit can be installed, that is by having the lead-in wire connectedto the central lead 3, it is necessary for the workman to remove the end of the tubular sheath and the insulation within such end. Since the tubular sheath 1 is-ordinarily formed of a high abrasive resistant material such as steel, the only practical way in which a workman could sever the sheet would be by the use of a hacksaw. When using such a tool, however, there is always danger that'the workman will saw into the unitfarther than he should and damage the leadin cable or wire 3.

In accordance with the present invention, the end of the resistance unit formed in the manner previously described with all three components extending uniformly to the endindicated at 4 'is placedbetween opposed knives which form a part of a pair of dies. These dies with their cutting edges or knives are brought toward each other with the terminal of the heating unit there between so as to sever the sheath 1 in the manner illustrated in Fig. 4. The dies which may be used for this purpose have not been illustrated since many difierent forms may be employed, it being understood of course that dies with straight post cutting edges may not be used since otherwise in moving against the sheath from opposite sides and into the sheath for the purpose of severing the same they would contact and damage the central wire 3. Accordingly, the cutting edges of the dies should have a central relief area which may be curved or a single straight-sided notch so that as the knives come together they Will sever the sheath without cutting the wire 3. The knives are caused to move to gether so as to sever the sheath from the main body with the exception of two diametrically opposite wedging greater importance, such flattening causes a crushing of the hard packed insulation material and renders it friable to the point where it may be readily removed.

While the ends of the heating elements might be left in the flattened condition illustrated in Fig. 5 and shipped to the point of installation in that condition, I prefer to perform the further step of again placing the flattened end portion in a pair of dies which will reform the partially severed end of the sheath into substantially truly cylindrical condition as illustrated in Fig. 6.

Regardless of whether the end of the heating element is left in the condition of either Fig. 5 or Fig. 6, all that the workman need do when installing the same is to grasp the thus partially severed end with a pair of pliers and by slightly twisting the same, he will cause the sheath to break the bridging elements 5 and 6 releasing the end i of the sheath and at the same time stripping the crushed insulating material from the end of the lead 3. When this is done and the operation completed, the finished terminal ready for installation will be as illustrated in Fig. 7.

When a heating element is processed in the manner just described, the partially severed end of the sheath by virtue of its attachment to the bridging elements 5 and 6, will remain on the assembly protecting the end of the lead 3 to which the heating element will ultimately be connected to a lead-in cable and preserves also the insulating material within the partially severed portion of the sleeve, which in turn protects the undamaged portion of the insulating material in the main portion of the heating element adjacent the severed area.

By the utilization of the dies of the character described, the severing operation may be performed much more economically than for example by the use of an abrasive wheel or a lathe tool.

In many forms of heating units, the two ends to which electrical connection is to be made are relatively close together, so that it would be extremely diflicult to insert therebetween the type of cutting tools which have been used heretofore in stripping the ends of the sheath from the unit. By the procedure outlined above, however, the cutting operation can be performed even though the ends of the heating element are relatively closely spaced.

While the procedure outlined above has been described as being applied to only one of the ends of the heating element, it is to be understood, of course, that it may be applied to both ends and furthermore that the operation 4; on both ends may be conducted simultaneously since the type of die-cutting operation required makes this procedure possible.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

1, therefore, particularly point out and distinctly claim as my invention:

1. An electrical resistance unit of the type in which a tubular metallic sheath encloses a hard packed electrical insulation which supports a resistance heating element on the longitudinal axis of said sheath, characterized in that, in a circumferential area axially spaced by a short distance from theend of said sheath the latter has been severed except for minor bridges by which such terminal portion remains secured to the body of the sheath, and without impairment of the element therewithin, such terminal sheath portion thus being readily detachable for exposure of the element section shielded thereby.

2. An electrical resistance unit of the type in which a tubular metallic sheath encloses a hard packed electrical insulation which supports a resistance heating element on the longitudinal axis of said sheath characterized in that, in a circumferential area axially spaced by a short distance from the end of said sheath the latter has been severed except for minor diametrically opposite bridges by which such terminal portion remains secured to the body of the sheath, and without impairment of the element therewithin, such terminal sheath portion thus being readily detachable for exposure of the element section shielded thereby.

3. An electrical resistance unit of the type in which a tubular metallic sheath encloses a hard packed electrical insulation which supports a resistance heating element .on the longitudinal axis of said sheath characterized in that, in a circumferential area axially spaced by a short distance from the end of said sheath the latter has been severed except for minor bridges by which such terminal portion remains secured to the body of the sheath, and said insulation material enclosed by such partially severed terminal portion has been rendered friable by crushing, such partial severing of the unit being confined to the sheath to provide exposure of the element upon detachment of the terminal sheath portion.

4. An electrical resistance unit of the type in which a tubular metallic sheath encloses a hard packed electrical insulation which supports a resistance heating element on the longitudinal axis of said sheath characterized in that, in a circumferential 'area axially spaced by a short distance from the end of said sheath the latter has been severed except for minor diametrically opposite bridges by which such terminal portion remains secured to the body of the sheath, and said insulation material enclosed by such partially severed terminal portion has been rendered friable by crushing, such partial severing of the unit being confined to the sheath to provide exposure of the element upon detachment of the terminal sheath portion.

5. The method of conditioning for use the terminal portions of electrical heating units of the type in which a tubular metallic sheath encloses a hard-packed electrical insulation which supports a resistance heating element on the longitudinal axis of said sheath which comprises; engaging the opposite sides of said sheath at a short distance from an end thereof with cutting dies; forming such dies toward each other to sever such sheath except for small diametrically opposed bridges.

6. The method of conditioning for use the termina portions of electrical heating units of the type in which a tubular metallic sheath encloses a hard-packed electrical insulation Which supports a resistance heating element on the longitudinal axis of said sheath which comprises engaging the opposite sides of said sheath at a short distance from an end thereof with cutting dies; forcing such dies toward each other to sever such sheath except for small diametrically opposed bridges and to crush the hard packed insulation in the thus partially severed end portion of the sheath.

7. The method of conditioning for use the terminal portions of electrical heating units of the type in which a tubular metallic sheath encloses a hard-packed electrical insulation which supports a resistance heating element on the longitudinal axis of said sheath which comprises engaging the opposite sides of said sheath at a short distance from an end thereof with cutting dies; forcing such dies toward each other to sever such sheath except for small diametrically opposed bridges and at least partially flatten the thus partially severed terminal 1 tubular metallic sheath encloses a hard-packed electrical insulation which supports a resistance heating element on the longitudinal axis of said sheath which comprises engaging the opposite sides of said sheath at a short distance from an end thereof with cutting dies; forcing such dies toward each other to sever such sheath except for small diametrically opposed bridges, to at least partially flatten the thus partially severed terminal sheath and to crush the hard packed insulation therein and then, without rupture of said bridges, reforming such flattened end portion to substantially cylindrical condition.

References Cited in the file of this patent UNITED STATES PATENTS 1,157,916 Wentworth Oct. 26, 1915 1,972,411 Swartz et al Sept. 4, 1934 FOREIGN PATENTS 794,863 France Dec. 26, 1935 

